Preparation of triaryl phosphates



- producing substances.

Patented Sept. 12, 1944 2,358,133 PREPARATION or TRIARYL rnosrnn'rss Wesley C. Stoesser and Alexander H. Widiger, Jr., Midland, Micla, assignors to The Dow Chemical Company, Midland, Micht, a corporation of Michigan No Drawing. Application June 18, 1941,v Serial No. 398,572

4 Claims.

This invention relates to an improved method for the manufacture-of triaryl phosphates, particularly in forms free of acids and acid-forming impurities.

Triaryl phosphates are usually prepared by heating three molecular proportions of a phenol with one molecular proportion of a phosphorus oxyhalide, usually the oxychloride, and frequently in the presence of a metal salt catalyst. Mixed triaryl phosphates containing two or three different aryl groups in the molecule may be readily prepared by reacting phosphorus oxychloride simultaneously or consecutively with the necessary phenols. After the completion of the reaction, purification is usually accomplished by washing the reacted mixture with a dilute solution of an acid such as hydrochloric acid to remove traces of metal salts and with a dilute solution of an alkali such as sodium hydroxide to remove acidic constituents and finally with water. The washed material is then either distilled or crystallized.

In the preparation of triaryl phosphates by this usual method it is diflicult to secure a prodnot which is entirely free from acids or acid- This may be due to the formation in the reaction mixture of small amounts of compounds in which a part of the halogen in some of the phosphorus oxyhalide has not been replaced with an aryl group and to the gradual decomposition of such compounds in the presence of moisture or under the influence oi heat to liberate a hydrogen halide or phosphoric acid. The presence of such acid-producing substances is undesirable, since the phosphate products are often used for purposes where the presence of even a trace of acid is harmful. This is particularly true when the triaryl phosphates are used as plasticizers for resins.

We have found that the triaryl phosphates may readily and economically be produced in a form substantially free of acids and acid-producing impurities by reacting together the phosphorus oxyhalide and phenol, or phenols, as usual, to form the desired triaryl phosphate and blowing the crude reaction mixture with steam. The steaming facilitates removal of the halogen-containing or other acid-producing impurities, apparently by efiecting rapid hydrolysis or decomposition of such impurities into compounds which are readily removed from the phosphate product, e. g., by distillation or the usual washing operations.

Steaming of the crude product is carried out at temperatures between 100 and 200 0., usually between 120 and 190 impurities present. Steaming at too high a temfit 0., and preferably between 66 perature or for too long a period may result in excessive hydrolysis of the triaryl phosphate, and such a condition should, of course, be avoided. Under the stated conditions hydrolysis of the triaryl phosphate is practically negligible. Although the mixture may be steamed after washing, it is preferably steamed before being washed since the washing operations then serve to remove any alkalior acid-soluble compounds formed during the steaming. Alternatively, the hot crude phosphate product may be agitated with water at atmospheric or superatmospheric pressure, e. g., in an autoclave and at the above reaction temperatures, to cause reaction between the water and the impurities and convert the latter into compounds readily removable from the phosphate product. 4

After the treatment with steam or hot water is completed the mixture is preferably washed successively, and usually at 60-'l0 C., with a dilute aqueous acid solution, e. g., a 1.0 per cent solution of hydrogen chloride, a dilute aqueous alkali solution, e. g., a 1.0 per cent solution of sodium hydroxide, and water, and then distilled. Other water-soluble alkalies or mineral acids, e. g., Nazcos, KOH, K2003, or H2804, etc., may be used in the washing operations if desired. Removal of the metal salt catalyst is facilitated by washing with dilute acid, and suflicient dilute alkali should preferably be used to neutralize all free acid in the crude phosphate product. Any unreacted phenols may at least partially be removed by washing with alkali. Any remaining trace of alkali may be removed by the water wash. The distillation is usually carried out under vacuum and preferably in such a manner that a fore-fraction containing water and any unreacted phenol is collected and either discarded or subsequently reworked to recover the phenol. A pure triaryl phosphate fraction containing substantially no free acids or easily decomposable acid-producing substances is then collected.

Certain of the advantages of the invention will be seen from the following examples, which are illustrative and are not to be constructed as limiting the invention:

EXAMPLE 1 A serie of batches of crude triphenyl'phosphate were prepared by reacting together three molecular proportions of phenol and one molecular proportion of phosphorus oxychloride and each crude reacted mixture was divided into two equal parts. One part of each batch was subfrom acid or substances decomposable to form acids.

invention may be employed instead of the one phenyl phosphate fraction was substantially free mitted to purification in the ordinary manner, 5 explained, change being made as regards the i. e.,'by washing successively at 6040 C. with method herein disclosed, provided the step or steps an equal volume of a 1.0 per centhydrochlorie stated by any of the following claims or the acid solution, an equal volume of a 1.0 per cent equivalent of such stated step or'steps be emaqueous sodium hydroxide solution, and an equal ployed. volume of water. .-The' other part of each batch We therefore particularly point out and diswas heated to '155--160 0., steam was slowly tlnctly claimasour invention: passed through it i'or minutes, after which 1. In a method of making a, triaryl phosphate it was cooled to 60-70 C.,.and washed in the wherein aphenolic compound is reacted with "samemanner. After washing, the acidity of each Phosphorus oxychloride, the steps which comproduct was determined. The product was then .15 prise blowing steam through the reacted mixture iractionally distilled under vacuum. A small while maintaining the latter at a temperature tore-traction was first collected and the triphenyl between 120 and 190 C. whereby acid icrming phosphate was then collected separately. The insredients are ively de omposed. and then acidity oi each fraction of distillate was deterwashing the mixture with aqueous alkali to remined by analysis. The acidity values, calculated move acidic ingredients from the triaryl phosas weight per cent of Hal-"O4 and assuming that phate. the latter reacts as a dibasic acid, are listed below 2. In a method of making a triaryl phosphate in Table I. The unsteamed portions contained wherein a phenolic compound is reacted with appreciable quantities of free acid before distilling phosphorus oxychloride, the steps which comprise and this free acid perslstedinlboth the ioreblowing steam through the reacted mixture while fractions and the triphenyl' phosphate fractions. maintaining the latter at a temperature between In the caseof the steamed portions, the amount 140 and 170 C. whereby a i r g ingredients oi tree-acid present beforedistilling was extremeare selectively decomposed, and then washing the :ly low, and the amount of acid carried over into mixture with aqueous alkali to remove acidic inthe't'riphenyl phosphate fractions was sov small 3 :gredients from the triaryl phosphate.

as to be in most cases scarcely detectable. 8. In a method or makins rip y Phosphate Table I Y .Experimentl Experiments Ex eriments Percentagd cglculated as 5 4 Unsteamed Steamed Unstesmed Steamed Unstedmed Steamed In undistilled portion .Q. 1 '.0700 .0000 .0080 .0000 .0007 .0002 In fore-fraction .2240 0004 .3720 .0004' 0235 0000 In trlphenyl phosphate .0020 .0000 .0035 .0000 .0020 .0000

v Exlmrtl: 2 wherein phenol is reacted with phosphorus oxy- Three mols of phenol was heated together with zg gfi the steps which comprise blowing steam gh the reacted mixture while maintaining about'one'hau per cent of substantlany the latter at a temperature between 120 and 190 drous magnesium chloride to 95-105 C. and one I 0. whereby acid-forming ingredients are selecmol of DhO D oxychmflde was added gradu" tively decomposed, and then washing the mix- The temperature was raised gradually ture with aqueous alkali to remove acidic ingredi- 155 C., at which temperature the reaction was ems from the tripheny1phsphate finished. Steam was blown slowly through the 4 In a method f making a triaryl phosphate reacted mixture for twenty minutes while mainwherein a phenolic compound is reacted with taming the temperature at The phosphorus oxychloride, the steps which comprise Product was cooled 120 and Washed treating the reacted mixture with water at a ively w an equal volume h of a temperature between and c. whereby p r c t yd o i acid 50111151011, a Per ent 55 acid-forming ingredients are selectively decomsodium hydroxide solution, and water. The prodos d, and m n washing t mlxtme it aqueuct was then distilled under vacuum and a small ous alkali to remove acidic ingredients from the tore-fraction consisting principally of water and triaryl phosphate. unreacted phenol collected separately. The tri- WESLEY C. STOESSER.

" ALEX. H. WDIGER, JR. 

